营养不良（英语：malnutrition）是一个描述健康状况的用语，是指由不平衡饮食所造成的营养素缺乏、过剩、或比例失调。重要的营养成分包括：产生热量的蛋白质、脂质与糖类，还有不产生热量的维生素与膳食矿物质。一般会用「营养不良」指称营养不足，也就是摄取的热量、蛋白质与微量元素不足，但营养过剩也属于营养不良的一种。若是孕妇在怀孕时或儿童在两岁以前发生营养不足，可能会对儿童的身心发展造成永久性的损伤。极度的营养不足称之为饥馑，处在饥馑状态的人可能会有身高偏低、体型瘦弱、活力不佳、腿部及腹部肿胀的情形，也容易受到疾病感染且不耐寒冷，而微量元素缺乏产生的症状则视缺乏的元素而各有不同。如果不能长期摄取由适当数量、种类或质量的营养素所构成的健康饮食，个体将产生营养不良。长期的营养不良可能导致饥饿死亡。

Malnutrition or malnourishment is a condition that results from eating a diet in which nutrients are either not enough or are too much such that the diet causes health problems. It may involve calories, protein, carbohydrates, vitamins or minerals. Not enough nutrients is called undernutrition or undernourishment while too much is called overnutrition. Malnutrition is often used specifically to refer to undernutrition where there is not enough calories, protein, or micronutrients. If undernutrition occurs during pregnancy, or before two years of age, it may result in permanent problems with physical and mental development. Extreme undernourishment, known as starvation, may have symptoms that include: a short height, thin body, very poor energy levels, and swollen legs and abdomen. People also often get infections and are frequently cold. The symptoms of micronutrient deficiencies depend on the micronutrient that is lacking.